Muskrat Falls reservoir levels reduced due to cofferdam seepage

Water seeped through a temporary cofferdam at the Muskrat Falls reservoir early Friday morning, according to Nalcor Energy, but the company says that doesn't mean there's a problem.

Communities, stakeholders notified, in according with emergency plan, says Nalcor

The Muskrat Falls cofferdam is a temporary barrier, and Nalcor says seepage is common. (Nalcor Energy)

There was "increased water seepage" from a temporary cofferdam at the Muskrat Falls reservoir early Friday morning, according to a statement from Nalcor Energy.

An engineering team inspected the cofferdam and recommended the reservoir levels be reduced to "mitigate risk associated with increased flow and to maintain the integrity of the cofferdam," according to a statement from Nalcor.

The Crown corporation opened the spillway gates, causing increased water flow downstream of the Muskrat Falls hydroelectric project.

Nalcor CEO Stan Marshall said Nalcor made the decision to bring down the water after noticing increased flow and discoloration of the water.

This drawing shows the layout of the temporary cofferdam at Muskrat Falls. (Nalcor Energy)

Once water levels are down, Nalcor said the cofferdam will undergo further inspection.

Nalcor said there is no risk of flooding in any surrounding communities, saying the water flow conditions are consistent with those during the spring season.

Communities and stakeholders were notified of the situation, in accordance with Nalcor's emergency preparedness plan, the company said.

Not meant to be waterproof

The Cofferdam is a temporary dam built slightly upstream from the planned permanent dam.

According to Nalcor CEO Stan Marshall, it's put in place to allow for construction of the real deal.

The rock-filled cofferdam is "not designed to be completely impervious," said Nalcor in second statement late Friday.

"A cofferdam is composed of rocks and soil materials. It's temporary. It normally would have some seepage" Marshall told CBC Radio's On The Go.

The Muskrat Falls hydroelectric project in Labrador. Nalcor says 'increased water seepage' was spotted at a temporary cofferdam early Friday morning. (Nalcor Energy)

The structure, which is 450 metres long and 26 metres high, spans a channel in the Churchill River.

Marshall said some seepage is expected, but the repair work could cause another delay in Muskrat Falls construction.

"Well it's certainly going to mean a delay which is of concern right now as we [head towards] winter," Marshall said.  "That is the most serious concern that it is going to jeopardize your schedule."